a) Field of the Invention
Up to the present time, the clearing out of joints in masonry ducts or conduits for renovation purposes has been carried out in practice by means of cutting tools or shaping toots which are generally driven by hand-held machine tools for mechanically removing the joint mortar from the joint. The widths of the joints and the strength of the mortar, whose composition is frequently unknown, vary widely. In every case, the mortar must be removed as far as possible over the entire width of the joint and over a joint depth which is at least twice as large as the joint width in order to restore statically sound stability to the conduit by subsequent repointing. The extremely poor working conditions prevailing in such conduits in general and particularly when clearing out joints (high noise and dust nuisance, poor air) can be improved only with great effort, so that such endeavors tend toward the automation of this work process in such a way that a direct operation of the machine tool in situ is no longer required and operation is effected via a control unit outside of the conduit.
b) Description of the Related Art
DE U1 90 04 589 proposes a device with a work vehicle which can travel in the longitudinal direction of the conduit to be renovated and which is outfitted with a renovation tool in the form of a cutter and with at least one camera and with an operating console arranged remote from the work vehicle for controlling the work vehicle. With a device of this kind, it is no longer necessary for a work force to stay in the conduit while the joints are cleared out. Nevertheless, all of the disadvantages associated with clearing out by means of mechanical tools basically persist:
high tool wear due to extensive continuous loading and high machining forces; PA1 high maintenance for the machine tools in order to prevent the effects on the driving accuracy and guiding accuracy of the workpiece caused by the resulting fine dust and to avoid impairment of the service life of the machine tool; PA1 relatively slow feed rate; PA1 along machining times,
e.g., the minimum removal depth cannot be achieved by means of cutters in one machining step, so that the joint must be reworked repeatedly when cutting is used. In the case of saws, both joint edges are sawed one after the other and the remaining web is subsequently chiseled out.
The disadvantages indicated above make the clearing out of joints a time-consuming and costly process. Elaborate steps taken to automate this process cannot decisively increase the effectiveness of the process as long as the clearing out of joints is carried out by means of mechanical tools.
Water jet cutting is a known nonmechanical process for removing or severing material. The corresponding devices differ essentially in the shape and arrangement of the nozzles depending on the respective use. For example, for surface-oriented removal of material or to clean surfaces, a plurality of nozzles are arranged relative to one another in a plane of a nozzle head in such a way that they direct the water jet in the same direction. The nozzle head is set in rotation by means of its own drive or by means of an external drive. When cutting stone, for example, only individual nozzles are used, wherein an abrasive is added to the water depending an the hardness of the material in order to increase cutting power. For this purpose, the distance of the nozzle from the surface and possibly the size of the nozzle opening is selected depending on the material and the cutting depth of the water pressure. The cutting width is essentially invariable.